This invention relates to a solar powered light assembly with automatic control of light output to adjust the output to accommodate the solar illumination available for recharging of assembly.
Commonly owned U.S. Pat. No. 6,013,985 issued Jan. 11, 2000 and entitled xe2x80x9cSEALED SOLAR-POWERED LIGHT ASSEMBLYxe2x80x9d, the disclosure of which is incorporated herein by reference, describes a permanently sealed solar-powered hazard light. The assembly uses a light emitting diode (LED) as an illumination source and offers dramatically improved reliability and vandal-resistant solar powered lighting by incorporating all the components of a solar-powered light into a single sealed unit. However, the single greatest inefficiency of this design is that the electronics must be optimised for the worst solar conditions that the light assembly is likely to encounter. In practical terms, this means that the light must be designed for the worst of the winter months when ambient light available for recharging the light assembly is lowest. The result is that in the summer, the light assembly operates relatively inefficiently, as the unit is unable to use much of the energy available for capture by the solar panels. Similarly, unless each light assembly is set up individually, there is no means of adjusting the light output level of the assembly to the installation location. For example, a light assembly used in Egypt, where there are 6 hours of sunlight on average every day, will have the same light output as a light assembly used in Patagonia which has only one hour of sunlight available per day to recharge the unit. The light used in Egypt therefore has a large inefficiency in which at least eighty percent of the incoming solar energy is not used.
Accordingly, there is a need for a lighting unit that that is able to automatically adjust its light output in response to the solar energy available to charge the light battery.
The present invention provides a solar-powered light assembly comprising:
at least one light-emitting diode (LED) powered by a rechargeable battery;
a solar panel to recharge the battery and to sense light levels; and
control circuitry to monitor the rechargeable battery at intervals and, at the start of an interval, set the at least one LED to output light at a pre-determined level based on the battery voltage at the start of said interval.
The present invention also provides a method of controlling a solar-powered light assembly having at least one light-emitting diode (LED) powered by a rechargeable battery and a solar panel to recharge the battery and to sense light levels, comprising the steps of:
monitoring the rechargeable battery at intervals;
setting the at least one LED to output light at a pre-determined level at the start of an interval based on the battery voltage at the start of said interval.
The apparatus and method of the present invention rely on a control system that determines the charge received by the batteries during the day from the solar panel which is dependent on ambient light levels, and uses this information to determine and set the light output level of the LEDs. By automatically altering the light output level, the light assembly of the present invention can produce its maximum light output during the summer months and then can reduce its output during the winter months when ambient light levels decline. This automatic light output control ensures that the light assembly continues to function reliably despite wide variations in solar illumination available to recharge the batteries. It also allows a single model of the solar-powered light assembly to be shipped to any location in the world, since the control scheme allows the light assembly to adapt to the ambient light levels available at its location adjusting the assembly""s light output level to be in balance with the solar energy available for recharging of the batteries.